TL;DR — Quick Summary

SUA IMSS error calculating bimonthly employer-employee social security contributions: fix integration factor, salary types, and database issues

When Mexico’s SUA (Sistema Único de Autodeterminación) from IMSS generates errors while calculating bimonthly employer-employee social security contributions, the result can be an incorrect payment file, fines for discrepancies, or the inability to meet employer obligations on time. This error directly affects the calculation of social security contributions that employers must pay to IMSS every two months, including sickness and maternity, disability and life, retirement, unemployment in old age, and old age insurance.

The Error

When running the calculation from Contribution Determination > Calculation, SUA displays one or more of these messages:

“Error al calcular cuotas obrero-patronales del bimestre seleccionado” (Error calculating employer-employee contributions for the selected bimonthly period)

“El SBC del trabajador no corresponde al período de cálculo” (The employee’s SBC does not match the calculation period)

“No se encontró factor de integración válido para el ejercicio” (No valid integration factor found for the fiscal year)

The error can manifest in several ways:

  • SUA completes the calculation but the resulting contributions do not match expected amounts
  • The system flags specific employees with calculation errors in the discrepancy report
  • The payment file (.SUA) is generated with zero amounts for some employees
  • The calculation is interrupted showing a database error

Root Cause

Bimonthly employer-employee contributions depend on four elements that must be correctly configured in SUA:

Incorrect integration factor. The integration factor determines how the Base Contribution Salary (SBC) is calculated from the daily wage. If the factor does not match the current fiscal year or the type of benefits the company offers (minimum legal vs. superior), all contributions will be calculated incorrectly. For 2026, the minimum legal factor is 1.0493.

Misconfigured salary type. SUA distinguishes between fixed, variable, and mixed salaries. If an employee with commissions is registered as fixed salary, the SBC will not include variable earnings and contributions will be lower than required. Conversely, a fixed-salary employee registered as variable will generate calculations with non-existent averages.

Incorrect work periods. When registration, termination, re-entry, or salary modification dates do not correspond to the calculated bimonthly period — or overlap each other — SUA cannot correctly determine the days contributed. This commonly happens when:

  • A re-entry is registered without first terminating the employee
  • Salary modification dates fall outside the bimonthly period
  • Duplicate movements exist for the same period

Database inconsistencies. The SUA database (SUA.MDB file in Microsoft Access format) can become corrupted by unexpected closures, power outages, or conflicts when using the program over a network. A damaged database produces erratic calculations or read errors during the process.

Step-by-Step Solution

1. Verify the integration factor

Open SUA and navigate to Configuration > Employer Data. Check the Integration Factor field and confirm it against the IMSS-published table:

Employee seniorityMinimum legal factor 2026
1 year1.0493
2 years1.0548
3 years1.0602
4 years1.0657

If your company offers benefits above the legal minimum (more vacation bonus days, higher Christmas bonus, etc.), the factor must be higher. Recalculate using the formula:

Factor = 1 + (Christmas Bonus Days/365) + (Vacation Days × Vacation Premium / 365)

2. Review the salary type for each affected employee

Go to Affiliation > Query/Modification and search for employees appearing in the error report. For each one verify:

  • Salary type: fixed, variable, or mixed
  • Registered SBC: must match the daily wage multiplied by the integration factor (for fixed) or the average of variable earnings from the previous bimonthly period (for variable)
  • SBC date: must fall within the bimonthly period being calculated

3. Correct work periods

In Affiliation > Affiliation Movements, review the timeline for each problematic employee:

  • Verify no two registrations exist without an intermediate termination
  • Confirm salary modifications have dates within the correct bimonthly period
  • Remove duplicate movements using Affiliation > Movement Deletion

4. Repair the database

Close SUA completely. Navigate to C:\CobranzaSUA\ and locate the SUA.MDB file. Before making any changes:

  1. Copy the file to a safe location as a backup
  2. Open the original file with Microsoft Access
  3. Run Tools > Database Utilities > Compact and Repair
  4. Close Access and reopen SUA

5. Run the recalculation

With corrections applied, return to Contribution Determination > Calculation. Select the correct bimonthly period and year. Run the calculation and review the discrepancy report before generating the final payment file.

Alternative Solution

If the error persists after manual corrections, you can recreate the bimonthly data:

  1. Export the information from the current bimonthly period using Utilities > Export Data
  2. Restore a clean backup of the database from Utilities > Restore Backup
  3. Re-import the corrected movements with Utilities > Import Data
  4. Recalculate from the restored database

Another option is to completely uninstall SUA, reinstall the latest version from the IMSS portal, and restore the backup. This resolves corrupted program file issues.

Prevention

  • Update the integration factor at the start of each fiscal year and whenever company benefits change
  • Enter affiliation movements immediately when they occur, do not accumulate them until the end of the bimonthly period
  • Create backups of the database before each bimonthly calculation using Utilities > Backup
  • Verify salary types for new employees at the time of registration
  • Compact the database at least once a month from Microsoft Access
  • Do not use SUA over a network without an established procedure to prevent simultaneous access to the .MDB file
  • Zero contributions for some employees: Usually caused by a variable salary type with no earnings captured in the previous bimonthly period. Register variable earnings before calculating.
  • Differences between SUA calculation and IMSS settlement: Verify that your SUA version has updated contribution tables. Download the latest update from IDSE.
  • “Employee has no contributed days” error: The registration movement has a date after the start of the bimonthly period, or a previous termination exists without re-entry.

Summary

  • SUA employer-employee contribution calculation errors originate from incorrect integration factor, misconfigured salary type, overlapping work periods, or corrupt database
  • Verify the integration factor against IMSS tables for the current fiscal year
  • Confirm that the salary type (fixed, variable, mixed) matches each employee’s actual pay structure
  • Repair the SUA.MDB database with Microsoft Access before recalculating
  • Perform frequent backups and enter affiliation movements promptly to prevent errors